Abstract
A beam deflector includes a magnetic-flux-guiding structure which has an opening through which a beam axis extends, and at least two coils arranged at the magnetic-flux-guiding structure so that they produce a magnetic field B.sub.1 having lines passing through the two coils in succession, leave the magnetic-flux-guiding structure at a first location on a first side in relation to the beam axis, cross the beam axis at a second location which is arranged at a distance along the beam axis from the magnetic-flux-guiding structure, re-enter into the magnetic flux-guiding structure at a third location on a second side lying opposite the first side, and extend around the opening from the third location to the first location within the magnetic-flux-guiding structure.
Claims
1. A particle-optical apparatus configured to influence a particle beam passing through the particle-optical apparatus along a beam axis, the particle-optical apparatus comprising: at least two coils, each having at least one turn, wherein: when the at least two coils carry current and other coils of the particle-optical apparatus do not carry current, the at least two coils produce a magnetic deflection field on the beam axis; a maximum distance of the at least one turn from the beam axis is a first distance; a magnetic flux density of the magnetic deflection field on the beam axis has a maximum of its absolute value which is located on the beam axis; the maximum of the absolute value of the magnetic flux density of the magnetic deflection field on the beam axis is arranged at a location along and on the beam axis which has a second distance from the turns measured along the beam axis; and the second distance is at least 0.02 times as large as the first distance.
2. The particle-optical apparatus of claim 1, further comprising a magnetic-flux-guiding structure having an opening through which the particle beam axis extends, wherein: the at least two coils are arranged at the magnetic-flux-guiding structure; and the magnetic-flux-guiding structure is configured to provide closed flux paths for the magnetic deflection field around the beam axis.
3. The particle-optical apparatus of claim 2, wherein a first group of the closed flux paths is arranged at a greater distance from the beam axis than the at least one turn of the at least two coils.
4. The particle-optical apparatus of claim 3, wherein a second group of the closed flux paths is arranged at a lesser distance from the beam axis than the at least one turn of the at least two coils.
5. The particle-optical apparatus of claim 2, wherein the closed flux paths do not include closed flux paths that are arranged at a lesser distance from the beam axis than the at least one turn of the at least two coils.
6. The particle-optical apparatus of claim 2, wherein a surface of the magnetic-flux-guiding structure comprises a plurality of surface regions, and the at least one turn of each of the coils is arranged at a surface region.
7. The particle-optical apparatus of claim 6, wherein the surface region extends toward the beam axis so that an edge of the surface region that is arranged closest to the beam axis is arranged closer to the beam axis than the at least one turn of the coil which is arranged at the surface region.
8. The particle-optical apparatus of claim 6, wherein at least one slot in the surface of the magnetic flux guiding structure extends radially outward relative to the beam axis proceeding from the edge that is arranged closest to the beam axis.
9. The particle-optical apparatus of claim 8, wherein the at least one slot extends between two coils that are adjacent to one another in a circumferential direction around the beam axis.
10. The particle-optical apparatus of claim 2, wherein the magnetic-flux-guiding structure comprises a metallic plate element carrying one or more of the at least two coils.
11. The particle-optical apparatus of claim 2, further comprising a power supply system, wherein: the at least two coils comprise first and second flat coils opposite one another on the magnetic-flux-guiding structure in a substantially symmetric manner relative to the opening; and the power supply system is configured to supply the first and second flat coils with current so that magnetic fields produced by the first and second flat coils are oriented in mutually opposite directions.
12. The particle-optical apparatus of claim 1, wherein the at least two coils are distributed about the beam axis in a circumferential direction.
13. A particle-optical apparatus configured to influence a particle beam passing through the particle-optical apparatus along a beam axis, the particle-optical apparatus comprising: at least two coils on both sides of the beam axis, wherein: each coil comprises at least one turn; when the at least two coils carry current and other coils of the particle-optical apparatus do not carry current, the at least two coils produce a magnetic deflection field (B.sub.⊥) on the beam axis, which has a centroid on the beam axis at a location z.sub.0; each of the at least two coils respectively has a center of mass at a location {right arrow over (r)}.sub.0; a ratio between a distance of the location z.sub.0 from a connecting line between the two locations {right arrow over (r)}.sub.0 and a distance of the two locations {right arrow over (r)}.sub.0 from one another is greater than 0.1; where integration is carried out along the beam axis extending in the z-direction, B.sub.⊥(z) is the component of the magnetic field (B.sub.1) on the beam axis oriented orthogonal to the beam axis and z.sub.min and z.sub.max are locations on the beam axis and delimit a region thereon, in which the values of B.sub.⊥(z) are greater than 0.01 times the and where integration is carried out along the current carrier forming the respective coil over the length L thereof, {right arrow over (r)} are the locations on the centre line of the current carrier forming the coil and {right arrow over (r)}.sub.s are locations in space.
14. The particle-optical apparatus of claim 13, further comprising a magnetic-flux-guiding structure having an opening through which the beam axis extends, wherein: the at least two coils are arranged at the magnetic-flux-guiding structure; and the magnetic-flux-guiding structure is configured to provide closed flux paths for the magnetic deflection field around the beam axis.
15. The particle-optical apparatus of claim 14, wherein a first group of the closed flux paths is arranged at a greater distance from the beam axis than the at least one turn of the at least two coils.
16. The particle-optical apparatus of claim 15, wherein a second group of the closed flux is arranged at a lesser distance from the beam axis than the at least one turn of the at least two coils.
17. The particle-optical apparatus of claim 14, wherein the closed flux paths do not include closed flux paths that are arranged at a lesser distance from the beam axis than the at least one turn of the at least two coils.
18. The particle-optical apparatus of claim 14, wherein a surface of the magnetic-flux-guiding structure comprises a plurality of surface regions, and the at least one turn of each of the coils is arranged a surface region.
19. The particle-optical apparatus of claim 18, wherein the surface region extends toward the beam axis so that an edge of the surface region that is arranged closest to the beam axis is arranged closer to the beam axis than the at least one turn of the coil which is arranged at the surface region.
20. The particle-optical apparatus of claim 18, wherein at least one slot in the surface of the magnetic flux guiding structure extends radially outward relative to the beam axis proceeding from the edge that is arranged closest to the beam axis.
21. The particle-optical apparatus of claim 20, wherein the at least one slot extends between two coils that are adjacent to one another in a circumferential direction around the beam axis.
22. The particle-optical apparatus of claim 13, wherein the at least two coils are distributed about the beam axis in a circumferential direction.
23. The particle-optical apparatus of claim 14, wherein the magnetic-flux-guiding structure comprises a metallic plate element carrying one or more of the at least two coils.
24. The particle-optical apparatus of claim 14, further comprising a power supply system, wherein: the at least two coils comprise first and second flat coils opposite one another on the magnetic-flux-guiding structure in a substantially symmetric manner relative to the opening; and the power supply system is configured to supply the first and second flat coils with current so that the magnetic fields produced by the first and second flat coils are oriented in mutually opposite directions.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Embodiments of the disclosure are explained in more detail below on the basis of figures, but the disclosure is not restricted to such embodiments. In the figures:
(2) FIG. 1 is a cross-sectional view of a particle-optical apparatus according to an embodiment;
(3) FIG. 2 is a plan view of the particle-optical apparatus from FIG. 1;
(4) FIG. 3 is a graph which shows a profile of a dipole field produced by the particle-optical apparatus from FIGS. 1 and 2 along a beam axis of the apparatus;
(5) FIG. 4 is a cross-sectional illustration, corresponding to FIG. 1, of a particle-optical apparatus according to a further embodiment;
(6) FIG. 5 is a cross-sectional illustration, corresponding to FIGS. 1 and 4, of a particle-optical apparatus according to an even further embodiment;
(7) FIG. 6 is a plan view of the particle-optical apparatus from FIG. 5;
(8) FIG. 7 is a cross-sectional illustration, corresponding to FIGS. 1, 4 and 5, of a particle-optical apparatus according to an even further embodiment;
(9) FIG. 8 is a plan view of the particle-optical apparatus from FIG. 7;
(10) FIG. 9 is a cross-sectional illustration, corresponding to FIGS. 1, 4, 5 and 7, of a particle-optical apparatus according to an even further embodiment;
(11) FIG. 10 is a plan view of the particle-optical apparatus from FIG. 9;
(12) FIG. 11 is a schematic illustration of a power supply system for coils of a particle-optical apparatus according to one embodiment;
(13) FIG. 12 is a plan view, corresponding to FIGS. 2, 6, 8 and 10, of a particle-optical apparatus according to a further embodiment;
(14) FIG. 13 is a cross-sectional illustration, corresponding to FIGS. 1, 4, 5, 7 and 9, of a particle-optical apparatus according to an even further embodiment;
(15) FIG. 14 is a plan view of the particle-optical apparatus from FIG. 13;
(16) FIG. 15 is a graph which shows a profile of a dipole field produced by the particle-optical apparatus from FIGS. 13 and 14 along a beam axis of the apparatus;
(17) FIG. 16 is a cross-sectional illustration, corresponding to FIGS. 1, 4, 5, 7, 9 and 13, of a particle-optical apparatus according to an even further embodiment; and
(18) FIG. 17 is a schematic cross-sectional illustration of a particle-optical system according to an embodiment.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
(19) An embodiment of a particle-optical apparatus is explained below on the basis of FIGS. 1 to 3. Here, FIG. 2 shows a plan view of the apparatus, FIG. 1 shows a cross section through the apparatus along the line I-I in FIG. 2 and FIG. 3 shows a curve of a magnetic field produced by the apparatus along a beam axis.
(20) The particle-optical apparatus 1 illustrated in FIGS. 1 and 2 includes a magnetic-flux-guiding structure 3 which has a substantially annular-disk-shaped form that is symmetric in relation to a main axis 5. A coordinate system 7 shown in FIGS. 1 and 2 is selected in such a way that the z-axis thereof is oriented parallel to the main axis 5 of the magnetic-flux-guiding structure and an annular-disk-shaped part 9 of the magnetic-flux-guiding structure 3 extends in the xy-plane of the coordinate system. The magnetic-flux-guiding structure in the illustrated embodiment further has a circular outer edge 11 and a central opening 13, which is delimited by an inner edge 15 of the annular-disk-shaped part 9. Four coils 19 are attached to a side 17, at the top in FIG. 1, of the annular-disk-shaped part 9, the coils each having one or more turns of a wire which is connected to a power supply that is not illustrated in the figures and that is configured to supply an adjustable current to each coil. If a current flows through a coil 19, the latter produces a magnetic field, as explained below.
(21) The four coils 19 are distributed around the main axis 5 in the circumferential direction and are arranged in a non-overlapping manner in such a way that each of the coils 19 encompasses a relatively large area of a quadrant on the face of the upper side 17 of the annular-disk-shaped part 9.
(22) The assumption is made that the lower coil 19 and the upper coil 19 shown in FIG. 2 do not carry current and the right coil 19 and the left coil 19 shown in FIG. 2 carry current, with arrows 21 in FIG. 2 indicating the direction of the current flow. This current flow produces a magnetic field B.sub.1 outside of the magnetic-flux-carrying structure 3, the magnetic field being illustrated in FIG. 1 by four exemplary field lines 23.sub.1, 23.sub.2, 23.sub.3 and 23.sub.4. The field lines 23.sub.1, 23.sub.2, 23.sub.3 and 23.sub.4 emerge from the magnetic-flux-guiding structure 3 at locations 25.sub.1, 25.sub.2, 25.sub.3 and 25.sub.4 on the upper side 17 of the annular-disk-shaped part 9 and re-enter the magnetic-flux-guiding structure 3 at locations 27.sub.1, 27.sub.2, 27.sub.3 and 27.sub.4 on the upper side 17. Here, the locations 27.sub.1 and 25.sub.1, locations 27.sub.2 and 25.sub.2, 27.sub.3 and 25.sub.3 and also 27.sub.4 and 25.sub.4 lie diametrically opposite one another in respect of the main axis 5. The field lines 23.sub.1 to 23.sub.4 cross the main axis 5 at locations 29.sub.1, 29.sub.2, 29.sub.3 and 29.sub.4, respectively. On the main axis 5, the field lines 23 are oriented in the x-direction and hence orthogonal to the main axis 5. It is clear that the magnetic field B.sub.1 has the symmetry of a dipole field on the main axis 5. Hence, this magnetic field B.sub.1 is suitable to ensure that a beam of charged particles 31 directed onto the particle-optical apparatus 1 along the main axis 5 from the top in FIG. 1 experiences a deflection such that the particle beam is deflected at an angle α in the y-direction in relation to the main axis 5 when it emerges from the particle-optical apparatus 1 after passing through the opening 13 in the magnetic-flux-guiding structure 3. The deflection in the y-direction is effectuated out of the plane of the drawing of the sectional illustration in FIG. 1. However, the deflection is illustrated as a bend in the line 31 representing the beam of charged particles in FIG. 1 in order to identify this deflection in the drawing.
(23) FIG. 3 shows a graph with a curve 32 which represents the strength of the x-component of the magnetic field B.sub.1 in millitesla as a function of the z-position in millimetres along the main axis 5. Here, the opposing coils 19 are excited by an ampere turn. It is clear from the curve 32 that a maximum of the field B.sub.x(z) along the main axis 5 has a maximum at a position z.sub.m of approximately 8 mm. The graph of FIG. 3 further plots the position in the z-direction of one of the coils 19 and of the magnetic-flux-guiding structure 3. A location z.sub.s within the coil 19, which is arranged closest to the maximum at z.sub.m in the case of a projection onto the main axis 5, is denoted by z.sub.s in FIG. 3 and it lies at approximately z=2 mm. It is clear that the maximum of the magnetic field B.sub.x(z) on the main axis 5 is arranged at a distance of approximately 6 mm from the coils that produce the magnetic field. A maximum distance from the main axis 5 assumed by locations arranged within the coils is denoted by r.sub.max in FIG. 2 and it is approximately 44 mm. Consequently, a ratio
(24)
is approximately 0.14 and hence greater than 0.02, in particular greater than 0.05, in particular greater than 0.07 and in particular greater than 0.10.
(25) Hence, the particle-optical apparatus 1 can be used to influence a particle beam 31, which extends along the main axis 5 towards the particle-optical apparatus 1, in regions along the main axis 5 which are arranged at a distance from the components 9, 19, which form the particle-optical apparatus, along the main axis 5. This property of the spatial separation along the main axis of the components forming the particle-optical apparatus and of the locations at which the magnetic field produced by these components acts on the particle beam opens up new fields of use for the particle-optical apparatus in particle-optical systems and increases the flexibility in the development of novel particle-optical systems.
(26) This property is also shown in the geometric relation explained below: FIG. 3 plots a location z.sub.0 at which the magnetic field that is oriented orthogonally to the beam axis has its centroid. This centroid can be calculated using the following formula:
(27)
(28) The limits of integration z.sub.min and z.sub.max should be selected according to circumstances. It is clear from FIG. 3 that no significant contributions to the integrals arise outside of the range between −2 mm and +60 mm, and so this region can be selected to be the area of integration. It is also possible to select other values for z.sub.min and z.sub.max such as −100 mm and +100 mm, for example.
(29) In the example explained here, z.sub.0 equals 16 mm. Further, FIG. 3 shows a location {right arrow over (r)}.sub.0, at which the geometry of the coil 19 has an action centroid. This location can be calculated according to the following formula that was explained above:
(30)
(31) In the example explained, this location {right arrow over (r)}.sub.0 has a distance of 16 mm from the z-axis. In FIG. 3, reference sign 20 denotes a connecting line between the location {right arrow over (r)}.sub.0, which is calculated on the basis of the geometry of the coil 19, and a location not illustrated in FIG. 3, which was calculated from the geometry of the coil lying opposite the coil 19 shown in FIG. 3 in relation to the beam axis and which describes the focus of the action thereof. On account of the symmetry of the coil arrangement shown in FIGS. 1 and 2, this line 20 is orthogonal to the z-axis in FIG. 3 and intersects the latter. However, this need not be the case in general. The line 20 has a length of 32 mm and a distance of 15 mm from the location z.sub.0. Hence, the ratio of the distance of the location z.sub.0 from the connecting line 20 to the length of the connecting line 20 or to the distance of the locations {right arrow over (r)}.sub.0 of the two coils 19 from one another has a value of 0.47. The magnitude of this value also demonstrates the property of the particle-optical apparatus to the effect of being able to provide an effective deflecting magnetic field outside of the structure that produces the magnetic field.
(32) The field lines of the magnetic field produced by the coils 19 must be closed. In FIG. 2, two lines 35 illustrate how the field line 23.sub.2, shown in FIG. 1 in an exemplary manner, extends within the magnetic-flux-guiding structure, after the entry thereof into the latter at the location 27.sub.2, to the location 25.sub.2, from where it emerges from the magnetic-flux-guiding structure 3. Accordingly, the field line divides after its entry at the location 27.sub.2 and, within the magnetic-flux-guiding structure, extends around the opening 13 in the magnetic-flux-guiding structure 3 to the location 25.sub.2.
(33) Further, in FIG. 2, a minimum distance from the main axis 5, which locations within the coils 19 assume, is denoted by r.sub.min. A distance from the main axis 5 of the location 25.sub.1, at which the field line 23.sub.1 shown in an exemplary fashion emerges from the magnetic-flux-guiding structure 3, is denoted by d.sub.1 and the distance from the main axis 5 of the location 27.sub.1, at which this field line 23.sub.1 enters into the magnetic-flux-guiding structure 3, is denoted by d.sub.3. What applies to all field lines shown in an exemplary manner in FIG. 1 is that d.sub.1 is greater than r.sub.min and that d.sub.3 is greater than r.sub.min. This also corresponds to the fact that the field lines shown in an exemplary manner pass through the two coils that lie opposite one another in respect of the main axis 5 in succession.
(34) In FIG. 1, a distance along the main axis 5 from the magnetic-flux-guiding structure 3 of the location 29.sub.1, at which the field line 23.sub.1 shown in an exemplary fashion crosses the main axis 5, is denoted by d.sub.2. In the case of the symmetry of the magnetic-flux-guiding structure 3 and of the coils 19 shown in FIGS. 1 and 2, d.sub.1=d.sub.3 applies. However, this need not be satisfied in the case of developments of the geometries of the magnetic-flux-guiding structure and of the coils. Further, it is possible to form the ratio
(35)
to be precise for every possible field line of the field B.sub.1 which emerges from the magnetic-flux-guiding structure 3 at a first location (25), crosses the main axis 5 at a second location (29) and re-enters the magnetic-flux-guiding structure 3 at a third location (27). For the field line 23.sub.1 shown in FIG. 1 in an exemplary manner, x=0.385 applies, x=0.415 applies to the field line 23.sub.2, x=0.505 applies to the field line 23.sub.3 and x=0.660 applies to the field line 23.sub.4. From this, it is clear that the magnetic field B.sub.1 has field lines for which the ratios x.sub.1 and x.sub.3 are greater than 0.5, in particular greater than 0.7 and in particular greater than 1.0. However, these conditions need not apply to all field lines of the magnetic field B.sub.1. The values of these ratios likewise embody the property of the profile of the magnetic field, shown in FIG. 3, along the main axis 5, according to which the magnetic field influences the particle beam 31 in regions that are arranged at a distance along the main axis 5 from the components 9, 19 that form the particle-optical apparatus 1.
(36) The profile of the magnetic field B.sub.1 is achieved by virtue of each of the coils 19, on their own, producing a magnetic field which is illustrated in FIG. 1 by vectors {right arrow over (B)}.sub.s. It is clear from FIG. 1 that the magnetic field {right arrow over (B)}.sub.s produced by each coil 19 has an orientation parallel to the main axis 5. In practice, the magnetic field {right arrow over (B)}.sub.s need not be oriented exactly parallel to the main axis 5, and, depending on the configuration of the magnetic-flux-guiding structure, it may be oriented, for example, at an angle of a few degrees in relation to the main axis 5 such that, nevertheless, a predominant component of the magnetic field {right arrow over (B)}.sub.s is oriented in the direction of the main axis 5. This fact leads to the magnetic field having field lines which cross the main axis 5 at a comparatively large distance along the axis 5 from the components of the apparatus 1.
(37) The vector {right arrow over (B)}.sub.s characterizing the magnetic field of each one of the coils 19 can be determined as follows: initially, a location {right arrow over (r)}.sub.s at which the vector {right arrow over (B)}.sub.s is attached with its foot or its tip in the region of the respective coil 19 is determined. The location {right arrow over (r)}.sub.s can be determined by virtue of calculating the centre of mass of the respective coil over a linear integral along the turns of the coil, according to formula (1) below:
(38)
(39) Here, L denotes the length of the wire forming the turns of the coil, which extends along the curve {right arrow over (r)}(l) in space, where 0≤l≤L.
(40) The magnetic field {right arrow over (B)}({right arrow over (r)}).sub.s at the location {right arrow over (r)}.sub.s can then be determined by numerical simulation, for example using a finite-element method.
(41) Further embodiments of the particle-optical apparatus are described below on the basis of further figures. In the following description, components that correspond to the components shown in FIGS. 1 to 3 in respect of the properties and/or functions thereof are denoted by the same reference sign. Generally, differences between the various embodiments will be explained and the description of similarities is omitted in order to obtain a desired conciseness of the description. Therefore, reference should be made to the description above and the description below for the purposes of understanding each embodiment.
(42) FIG. 4 shows a cross section, corresponding to FIG. 1, through a particle-optical apparatus 1 according to a further embodiment. This particle-optical apparatus 1 also includes four coils 19, which are arranged in distributed fashion around a main axis 5 in the circumferential direction, and a magnetic-flux-guiding structure 3, which has a central opening 13. In contrast to the particle-optical apparatus in FIG. 1, a body 9 that forms the magnetic-flux-guiding structure 3 is embodied not with the geometry of a flat disc but with that of a cone. Accordingly, the turns of the coils 19 are not arranged in a planar fashion in the xy-plane but along a curve extending with curvature in space.
(43) Vectors {right arrow over (B)}.sub.s which characterize a magnetic field that is produced by each one of the coils 19 are also illustrated in FIG. 4. On account of the conical configuration of the body 9 that forms the magnetic-field-guiding structure 3, the vectors {right arrow over (B)}.sub.s are not oriented parallel to the main axis 5, like in FIG. 1, but at an angle β thereto. This angle β is less than 60°, in particular less than 50° and in particular less than 40° and leads to field lines of the produced magnetic field crossing the main axis 5 at a distance along the main axis 5 from the magnetic-flux-guiding structure.
(44) This property of the magnetic field {right arrow over (B)}.sub.s respectively produced by the coils can also be obtained in the case of other geometries of the magnetic-flux-guiding structure and of the coils than those shown in FIGS. 1, 2 and 4. In respect of its design, the body 9 that forms the magnetic-flux-guiding structure 3 can be greatly varied, for as long as the condition is met that an angle between the main axis 5, along which a charged particle beam may also extend during the operation for influencing purposes, and the vector {right arrow over (B)}.sub.s is less than 60°, less than 50° or less than 40°. In the geometry shown in FIG. 4, the use of equation (1) above for calculating the location {right arrow over (r)}.sub.s at which the foot or the tip of the vector {right arrow over (B)}.sub.s is attached is inexpedient since, if formula (1) is used, the calculated value {right arrow over (r)}.sub.s, which corresponds to the centre of mass of the coil 19, would be arranged at the lower side 18 of the cone 9, where no magnetic field is produced in the vacuum. Here, it is advantageous to determine the location {right arrow over (r)}.sub.s by virtue of searching for the maximum of the absolute value of the magnetic field produced by the coil 19 in the surroundings of the particle-optical apparatus 1. This can be carried out experimentally or by way of numerical simulation for a sufficient multiplicity of different locations in the surroundings of the apparatus and selection of the location at which the respectively calculated magnetic field has its largest absolute value. This method for calculating the location {right arrow over (r)}.sub.s can also be used in the case of the apparatus explained on the basis of FIGS. 1 to 3 and in the case of the apparatuses explained below. This may yield a slightly different location {right arrow over (r)}.sub.s than in the case of the calculation using formula (1), having as a consequence a slightly different vector {right arrow over (B)}.sub.s as well; however, what will also apply to the vector is that the angle of the vector in relation to the main axis 5 will be less than 60°, less than 50° or less than 40°.
(45) The locations {right arrow over (r)}.sub.0, explained above, which were calculated according to the formula explained above, are also plotted in FIG. 4. These locations describe properties of the geometry of the coils 19 and coincide with locations which would emerge in the case of an appropriate application of the Biot-Savart formula for calculating magnetic fields. However, it is clear that substantially no magnetic field is present at the location {right arrow over (r)}.sub.0 on account of the magnetic-flux-guiding structure since the coil 19 is not an air coil.
(46) A further embodiment of a particle-optical apparatus 1 is shown in FIGS. 5 and 6; to be precise in a plan view in FIG. 6 and in cross section along the line V-V, found in FIG. 6, in FIG. 5. The configuration of the particle-optical apparatus 1 of FIGS. 5 and 6 is largely similar to the configuration of the particle-optical apparatus explained on the basis of FIGS. 1 to 3, but substantially differs from the latter in that slots 41 are provided in the ring plate 9 that forms the magnetic-flux-guiding structure 3, the slots, proceeding from the inner edge 15 of the opening 13 in the magnetic-flux-guiding structure 3, extending radially to the outside with respect to the main axis 5. These slots 41 modify the magnetic resistance of the magnetic-flux-guiding structure 3 in relation to the magnetic field flux. In particular, the slots 41 prevent the profile of field lines as illustrated in FIG. 2 by the lines 35. This magnetic resistance leads to a part of the field line 23.sub.2, that is shown in an exemplary fashion in FIG. 5 and enters the magnetic-flux-guiding structure 3 at the location 27.sub.2, extending along a line, denoted by 43 in FIG. 6, around the opening 13 and the slots 41 in order to arrive at the location 25.sub.2, at which it emerges from the magnetic-flux-guiding structure 3 again. A second part of field lines extends within the magnetic-flux-guiding structure 3 from the location 27.sub.2 to the main axis 5, emerges at the edge 15 of the opening 13 from the magnetic-flux-guiding structure 3, crosses the main axis in the vacuum and thereafter re-enters into the magnetic-flux-guiding structure by the edge 15 in order to arrive at the location 25.sub.2.
(47) Consequently, two types of flux paths arise within the magnetic-flux-guiding structure, wherein the one type, illustrated in an exemplary manner by the lines 43 in FIG. 6, extends around the opening 13 and the other type, illustrated in an exemplary manner by the line 45 in FIG. 6, passes through the opening 13 and consequently leads to a magnetic field B.sub.2 on the main axis 5, which likewise influences the particle beam 31 passing through the particle-optical apparatus 1. In FIG. 5, this magnetic field B.sub.2 is illustrated by three exemplary field lines 47. As a result of this magnetic field B.sub.2, the particle beam 31, after having being deflected in a direction by the magnetic field B.sub.1 that is formed at a distance along the axis 5 from the apparatus 1, is deflected in a direction opposite thereto when passing through the opening 13 in the magnetic-flux-guiding structure 3. The absolute values of the deflection angles produced by the field B.sub.1 and the field B.sub.2 need not be equal. FIG. 5 illustrates a situation in which the absolute values of these deflection angles are the same, however, and so the particle beam 31 extends parallel to the main axis 5 again after passing through the particle-optical apparatus 1, the particle beam also having approached the particle-optical apparatus 1 along the main axis. However, after passing through the particle-optical apparatus 1, the particle beam 31 is offset by an absolute value m in the y-direction in relation to a straight line along which it approached the particle-optical apparatus 1. The deflection in the y-direction is effectuated out of the plane of the drawing of the sectional illustration in FIG. 5. However, like in FIG. 1, the deflections are illustrated in FIG. 5 as bends in the line 31 representing the beam of charged particles in order to identify these deflections in the drawing.
(48) A further embodiment of a particle-optical apparatus is now explained on the basis of FIGS. 7 and 8, wherein FIG. 8 shows a plan view of the particle-optical apparatus 1 and FIG. 7 shows a cross section along the line VII-VII in FIG. 8. The particle-optical apparatus 1 illustrated in FIGS. 7 and 8 substantially differs from the particle-optical apparatus illustrated in FIGS. 5 and 6 in terms of the configuration of the slots 41, which are provided in a ring plate 9 that forms the magnetic-flux-guiding structure 3. In comparison with FIG. 6, the slots 41 in FIG. 8 extend further in the radially outward direction in respect of a main axis 5 of the apparatus and also in part extend in the circumferential direction there. This leads to the magnetic flux path illustrated by the lines 43 in FIG. 6, which extends around the opening 13, experiencing an even higher magnetic resistance. In comparison with the embodiment of FIGS. 5 and 6, this leads to an even greater proportion of field lines extending along the flux path illustrated by the line 45 in FIG. 6 and emerging from the magnetic-flux-guiding structure 3 at the edge 15 of the opening 13, crossing the main axis 5 and then re-entering the magnetic-flux-guiding structure 3. This, in turn, leads to the strength of the magnetic field B.sub.2 increasing relative to the strength of the magnetic field B.sub.1 in comparison with the embodiment shown in FIGS. 5 and 6. In FIG. 7, this is represented by virtue of four exemplary field lines 47 being illustrated for the magnetic field B.sub.2, in contrast to the three exemplary field lines 47 for the magnetic field B.sub.2 shown in FIG. 5.
(49) From a comparison between the embodiments illustrated on the basis of FIGS. 5 and 6 on the one hand and the embodiments illustrated on the basis of FIGS. 7 and 8 on the other hand, it is clear that the ratio of the effects exerted by the magnetic fields B.sub.1 and B.sub.2 on the particle beam passing through the apparatus can be adjusted by the geometric design of the slots 41 in the magnetic-flux-guiding structure. This leads to the particle beam passing through the particle-optical apparatus experiencing two deflections in mutually opposite directions in succession, wherein the ratio of the absolute values of the respective deflection angles can be set by the geometry of the slots 41 in the magnetic-flux-guiding structure 9. By setting the current flowing through the turns of the coils 19, it is possible to modify the magnitude of the respective deflection angle, with the ratio of the absolute values of the deflection angles, however, being maintained.
(50) Now FIGS. 9 and 10 are used to explain an embodiment in which it is also possible to set the ratio of the absolute values of the deflection angles of the two successive deflections experienced by the particle beam by way of the magnetic fields B.sub.1 and B.sub.2. Here, once again, FIG. 10 is a plan view of the particle-optical apparatus and FIG. 9 is a cross-sectional view along the line IX-IX in FIG. 10.
(51) The particle-optical apparatus 1 of FIGS. 9 and 10 once again has four coils 19 of the type as explained in the preceding embodiments. The magnetic-flux-guiding structure once again has a substantially annular-disc-shaped structure. However, it is made up of individual elements in this case, namely four sector-shaped plates 9.sub.1, 9.sub.2, 9.sub.3 and 9.sub.4 and outer rings 51, to which the sectors 9.sub.1 to 9.sub.4 are connected by screws 53. The sectors 9.sub.1 to 9.sub.4 are held by the outer rings 51 in such a way that they are not in contact and that, as a result thereof, slots 41 once again exist in the magnetic-flux-guiding structure 3 between the sectors, the slots increasing the resistance of magnetic flux paths around the opening 13. However, the outer rings 51 provide magnetic flux paths which extend around the opening 13. The magnetic resistance of these flux paths can be increased further by virtue of manufacturing the outer rings 51 from a material which has a relatively low magnetizability. In particular, the magnetizability of the material from which the outer rings 51 are manufactured may be less in this case than the magnetizability of the material from which the sector-shaped plates 9.sub.1, 9.sub.2, 9.sub.3 and 9.sub.4 are manufactured.
(52) Each of the sector-shaped plates 9.sub.1 to 9.sub.4 carries one of the coils 19 of this first type, as is also the case in the embodiments explained above. Moreover, each of the sector-shaped plates 9.sub.1 to 9.sub.4 carries a coil 55 of a second type. The coils 55 may, in turn, have one or more turns and are arranged on the outer edge of the plates 9.sub.1 to 9.sub.4 in relation to the main axis 5 and are wound around the respective plate such that the turns of the coils 55 extend not only along the upper side 17 of each plate 9 but also along the lower side 18 thereof.
(53) Consequently, a current flow through the right-hand coil 55 in FIG. 10 and through the left-hand coil 55 in FIG. 10 produces field lines which extend toward the main axis 5, for example in the plate 9.sub.2, emerge at the edge 15 of the opening 13 in the magnetic-flux-guiding structure 3 from the latter, cross the main axis 5 and re-enter the magnetic-flux-guiding structure 3 again at the opposite side, and consequently contribute to the magnetic field B.sub.2, illustrated by the field lines 47 in FIG. 9, for deflecting the particle beam when passing through the opening 13.
(54) Then, these field lines extend further in the plate 9.sub.4 in the radially outward direction, pass through the coil 55 arranged to the left in FIG. 10 and then extend back through the outer ring 51 to the coil 55 that is arranged at the right and illustrated in FIG. 10. The coil 55 arranged the left in FIG. 10 is not illustrated in FIG. 10 in order to make the configuration of the part of the plate 9.sub.4 that carries the coil 55 visible.
(55) Consequently, it is possible to set the ratio of the absolute values of the deflection angles of the deflections experienced in succession by the particle beam 31 when passing through the magnetic fields B.sub.1 and B.sub.2 by way of the ratio with which the coils of the first type 19 and the coils of the second type 55 are excited with the currents supplied thereto. A power supply system 57 suitable to this end is illustrated schematically in FIG. 11. This power supply system 57 supplies two coils 19 of the first type, lying opposite one another in respect of the main axis 5, and two coils 55 of the second type, likewise lying opposite one another in respect of the main axis 5. These four coils 19, 55 are supplied by a single power source 59, the current provided thereby being adjustable. A divider resistor 63 is connected to the power source 59 parallel to the coils 19, 55. A resistor 61 connects the point between the coils 19 and 55 and a division point of the divider resistor 63. By changing the resistance 63, it is possible to modify the ratio of the currents supplied to the coils 19 of the first type and to the coils 55 of the second type. This leads to a change in the ratios of the absolute values of the deflection angles of the two deflections by way of the magnetic fields B.sub.1 and B.sub.2. By changing the current provided by the power source 59, it is possible to modify the deflection angles while maintaining the ratio thereof that is predetermined by the resistance 63.
(56) However, it is also possible to supply the coils 19 and 55 from separate power sources. This leads to greater flexibility since the sign of the ratio of the currents supplied to the coil pair 19 and the coil pair 55 is also adjustable. Then, it is also possible for the deflection by the coil pair 19 to be effectuated in different direction in the xy-plane than the deflection by the coil pair 55. In such a case, the beam emerging from the particle-optical apparatus is skew in relation to the beam entering the particle-optical apparatus.
(57) In the embodiments explained above, the particle-optical apparatus 1 in each case has four coils 19 of the first type, with the coils 19 respectively illustrated to the left and right in FIGS. 2, 6, 8 and 10 having current flowing therethrough in such a way that a dipole field that is oriented in the x-direction arises on the main axis 5. The orientation of this dipole field in the circumferential direction around the main axis can be modified by virtue of current also being supplied to the coils 19 illustrated top and bottom in FIGS. 2, 6, 8 and 10. If current were only supplied to the coils 19 illustrated top and bottom in these figures, the coils would produce a dipole field oriented in the y-direction on the main axis 5. By setting the ratio of the currents supplied to the coils illustrated on the left and on the right on the one hand and to the coils illustrated at the top and at the bottom on the other hand, it is possible to set the orientation of the dipole field produced on the main axis in the circumferential direction about the main axis as desired.
(58) FIG. 12 shows a further embodiment of a particle-optical apparatus 1 in an illustration in a plan view, which corresponds to the illustrations in FIGS. 2, 6, 8 and 10. In contrast to the embodiments explained above, the embodiment of the particle-optical apparatus illustrated in FIG. 12 does not include four but eight coils 19 of the first type, which are arranged distributed around the main axis 5 of the particle-optical apparatus in the circumferential direction. By supplying suitable currents to these eight coils 19, it is possible to produce a magnetic field B.sub.1 which can act on a particle beam along the beam axis 5 at a distance from the particle-optical apparatus 1 and which has the symmetry of a dipole field or of a quadrupole field or of a quadrupole field that has a dipole field superposed thereon, which is adjustable in view of its strength and orientation about the main axis 5. By way of example, using such a quadrupole field, it is possible to modify the astigmatism of the particle beam passing through the particle-optical apparatus 1.
(59) FIG. 3 was used to explain that the maximum of the magnetic field B.sub.1, produced by the coils 19 of the first type, is arranged along the main axis 5 at a distance from the components 19, 9 of the particle-optical apparatus. FIGS. 13, 14 and 15 are now used to explain an embodiment of a particle-optical apparatus 1, in which this distance is adjustable. Here, FIG. 14 shows an illustration corresponding to FIGS. 2, 6, 8 and 10, which shows a plan view of the particle-optical apparatus 1, FIG. 13 shows the particle-optical apparatus in a section along the line XIII-XIII in FIG. 14 and FIG. 15 shows an illustration corresponding to FIG. 3, which shows profiles of magnetic fields, produced by this apparatus, along the main axis 5. In contrast to the embodiments explained above, the particle-optical apparatus 1 explained on the basis of FIGS. 14 and 15 has two different sorts of coils 19 of the first type, namely a first sort of coils 19.sub.1 and a second sort of coils 19.sub.2. Here, the coils 19.sub.1 of the first sort are arranged at a greater distance from the main axis 5 than the coils 19.sub.2 of the second sort. The coils 19.sub.2 of the second sort produce a magnetic field B.sub.12 which is illustrated by exemplary field lines 23.sub.12, 23.sub.22 and 23.sub.32 in FIG. 13. The coils 19.sub.1 of the first sort produce a magnetic field B.sub.11 which is illustrated in FIG. 13 by exemplary field lines 23.sub.41, 23.sub.51 and 23.sub.61. It is clear that the magnetic field produced by the coils 19.sub.1 of the first sort acts with a greater distance along the main axis 5 from the particle-optical apparatus 1 than the magnetic field B.sub.12 produced by the coils 19.sub.2 of the second sort. This also emerges from the graph of FIG. 15, which illustrates the profile of the magnitude of the magnetic field produced by the coils 19.sub.1 of the first sort upon excitation with an Ampere turn along the main axis 5 using a curve 23.sub.1 and the absolute value of the magnetic field B.sub.12 produced by the coils 19.sub.2 of the second sort upon excitation with an Ampere turn along the main axis as a curve 32.sub.2. The maximum of the curve 32.sub.1 lies at a position z.sub.m1 of approximately 8 mm and the maximum of the curve 32.sub.2 lies at a position z.sub.m2 of approximately 4 mm. Hence, the distance z.sub.m1−z.sub.s of the maximum of the magnetic field produced by the coils 19.sub.1 of the first sort from the components of the particle-optical apparatus is approximately 6 mm and the corresponding distance z.sub.m2−z.sub.s of the magnetic field produced by the coils 19.sub.2 of the second sort is approximately 2 mm. By setting the ratio of the current flow through the coils 19.sub.1 of the first sort and the coils 19.sub.2 of the second sort, it is consequently possible to modify the location of the maximum of the field, produced together by the coils 19.sub.1 and 19.sub.2, between z.sub.m2 and z.sub.m1 in a continuous manner.
(60) The coils 19.sub.1 of the first sort and the coils 19.sub.2 of the second sort can be excited by separate power sources in turn. However, it is also possible to respectively excite two coils 19.sub.1 of the first sort, lying opposite one another in respect of the main axis 5, and the coils 19.sub.2 of the second sort radially adjacent thereto by way of a single current source, as explained on the basis of FIG. 11. Then, two such power sources would be involved for the four coils 19.sub.1 of the first sort and the four coils 19.sub.2 of the second sort, as shown in FIG. 14. The location of the maximum of the fields produced together by the coils 19.sub.1 and 19.sub.2 can then be set by modifying the setting of the resistors 63 of the two circuits 57 according to FIG. 11.
(61) In the embodiments explained above, the coils 19 of the first type are respectively arranged on a single side of the magnetic-flux-guiding structure, namely on the upper side 17 of the magnetic-flux-guiding structure 3 in the illustrations of FIGS. 1, 5, 7, 9 and 13. FIG. 16 shows a section through an embodiment of a particle-optical apparatus 1, in which coils 19 of the first type are arranged both on the upper side 17 and on the lower side 18 of the magnetic-flux-guiding structure 3. The coils 19 arranged on the upper side 17 of the magnetic-flux-guiding structure 3 produce a magnetic field B.sub.2 which acts on the particle beam 31 above the magnetic-flux-guiding structure 3 in FIG. 16, as was also the case in the embodiments illustrated above. The coils 19 of the first type arranged on the lower side 18 of the magnetic-flux-guiding structure 3 produce a magnetic field B.sub.3 which acts on the particle beam 31 below the magnetic-flux-guiding structure in the illustration of FIG. 16. By way of an appropriate supply of currents to the coils 19, which are arranged on the upper side 17 and the lower side 18 of the magnetic-flux-guiding structure 3, it is possible to set the two magnetic fields B.sub.1 and B.sub.3 as desired in respect of the magnitude and orientation thereof. In particular, it is therefore possible, inter alia, to provide a so-called “double deflector” for the particle beam passing through the particle-optical apparatus 1.
(62) The embodiment illustrated in FIG. 16 can be developed further, for example by virtue of introducing slots 41 into the magnetic-flux-guiding structure 3. These slots 41, in turn, lead to the magnetic field B.sub.2 shown in FIGS. 5 and 7 arising in the region of the opening 13 in the magnetic-flux-guiding structure 3 such that, overall, it is possible to produce three magnetic fields B.sub.1, B.sub.2 and B.sub.3 for deflecting the particle beam. If, furthermore, coils 55 of the second type are additionally provided, each of the fields B.sub.1, B.sub.2 and B.sub.3 can be modified individually by mixing the coil currents in order to produce a “triple deflector”, in which three deflection angles are freely adjustable. By way of example, such a “triple deflector” can be used to selectively direct a particle beam onto two or more apertures or openings with different geometries in a plate, which is a arranged along the main axis 5 in the region of the opening 13, and to subsequently steer the particle beam back onto the main axis 5 again. Consequently, the openings with different geometries can act on the beam as different stops.
(63) FIG. 17 shows a particle-optical system 71 which includes an embodiment of the particle-optical apparatus 1 explained above. The particle-optical system includes a particle source 73 for producing a beam of charged particles which passes through the particle-optical system 71 along a main axis 5. The particle source 73 has a cathode tip 75, a suppressor electrode 77 and an extractor electrode 79. The charged particles emitted by the catheter tip 75 pass through an opening in the extractor electrode 79 and are accelerated towards an anode 81, pass through an opening in the anode 81 and enter into a beam tube 83. Further, the particle-optical apparatus 71 can have e.g. a stage, on which an object can be arranged, the particle beam being directed onto the object after passing through the beam tube 83 and an objective lens.
(64) The elements 75, 77 and 79 are insulated from one another by insulators 76, and the anode 81 is also electrically insulated by an insulator 82 from the rest of the system 71. According to one example, the potential of the catheter tip 75 is −20 kV, the potential of the suppressor electrode 77 is −20.3 kV, the potential of the extractor electrode is −16 kV and the potential of the anode 81 is 8 kV. A voltage supply for supplying these potentials to the various components is not illustrated in FIG. 17. The particle source 73 is arranged in an ultra-high vacuum in order to facilitate a field emission of electrons from the catheter tip 75. In practice, it is difficult to adjust the catheter tip 75, the suppressor electrode 77, extractor electrode 79 and the anode 81 with such great precision in respect of the main axis 5 that the produced particle beam also extends with the desired accuracy along the main axis. Further, it is desirable for the particle beam to pass through the condenser lens 85 centrally on the optical axis thereof in order to reduce the effect of lens aberrations on the focusing of the beam. Therefore, it is desirable to provide a beam deflector between the anode 81 and the condenser lens 85 in order to be able to set the position of the beam relative to the main axis 5.
(65) The particle-optical system illustrated in FIG. 17 further includes a condenser lens 85 for collimating the particle beam produced by the particle source 73. To this end, the condenser lens 85 has a coil body 87 and a pole shoe 89, which are arranged at a distance from one another and which produce a magnetic field which has the effect of a focusing round lens on the particle beam.
(66) Further, it is desirable to arrange the condenser lens 85 as close as possible to the particle source 73 in order to avoid strong widening of the beam upstream of the condenser lens 85. Therefore, an installation space for arranging the deflector, the installation space, in view of its extent along the main axis 5, being comparatively small, is available between the assembly of the condenser lens 85 and the assembly 81 of the anode with associated insulator 82. The particle-optical apparatus 1 explained above can advantageously be introduced into this restricted installation space in order to be used there as a beam deflector for adjusting the particle beam, with the magnetic field produced for the beam deflection acting in the region of the anode 81.
